Another update from ingydotnet^djgoku

Task/Average-loop-length/Scala/average-loop-length.scala

@@ -0,0 +1,37 @@
+import scala.util.Random
+
+object AverageLoopLength extends App {
+
+  val factorial: Stream[Double] = 1 #:: factorial.zip(Stream.from(1)).map(n => n._2 * factorial(n._2 - 1))
+
+  def expected(n: Int) = (for (i <- 1 to n) yield factorial(n) / Math.pow(n, i) / factorial(n - i)).sum
+
+  def trial(n: Int):Double = {
+    var count = 0
+    var x = 1
+    var bits = 0
+
+    while ((bits & x) == 0) {
+      count = count + 1
+      bits = bits | x
+      x = 1 << Random.nextInt(n)
+    }
+    count
+  }
+
+  def tested(n: Int, times: Int) = (for (i <- 1 to times) yield trial(n)).sum / times
+
+  val results = for (n <- 1 to 20;
+                     avg = tested(n, 1000000);
+                     theory = expected(n)
+  ) yield (n, avg, theory, (avg / theory - 1) * 100)
+
+
+  println("n          avg         exp      diff")
+  println("------------------------------------")
+  results foreach { n => {
+      println(f"${n._1}%2d    ${n._2}%2.6f    ${n._3}%2.6f    ${n._4}%2.3f%%")
+    }
+  }
+
+}